1. Field of the Invention
The present invention relates to a hydraulic and mechanical transmission apparatus arranged to achieve variable transmission of the power of a prime mover by means of cooperation between a hydrostatic continuously variable transmission having superior continuously variable transmission characteristics and a mechanical transmission device having superior transmission efficiency.
2. Description of the Related Art
A hydrostatic continuously variable transmission is already known from Japanese patent application Laid-open No. 63-83457. In the hydrostatic continuously variable transmission, a hydraulic pump and a hydraulic motor, at least either one of which is constructed as a variable displacement construction, are connected together by a hydraulic closed circuit, and an oil pump for supplementing the oil in the hydraulic closed circuit is driven by an input shaft which is a rotating shaft of the hydraulic pump.
However, in the above-described conventional hydrostatic continuously variable transmission, the oil pump is driven by a rotating shaft of the hydraulic pump which rotates at the same speed as the crankshaft of an engine, and therefore, if a sufficient discharge flow rate of oil is to be ensured in a low rotational speed region of the engine, it is necessary to increase the capacity of the oil pump. However, since the oil pump discharges oil in an amount proportional to its rotational speed, if the capacity of the oil pump is increased, the discharge flow rate of oil greatly exceeds the required amount in a high rotational speed region of the engine, and the driving force of the engine is wastefully consumed by that amount.